Clamps of the type used for clamping together several large sheets of paper, such as blueprints, are well-known and are in common use. Clamps of this type are usually closed by the pulling action of a pull member. The conventional method for pulling the pull member into its uppermost position to tighten the clamp and for holding the pull member in that position to keep the clamp closed is illustrated in U.S. Pat. No. 3,069,737, granted Dec. 25, 1962, to A. H. Schneider et al. This method employs a wing nut that engages the upper threaded end of the pull member and tightens against the upper surface of the clamp. This method has several disadvantages. First, since the wing nut is generally made of metal and is tightened against the surface of the clamp, it tends to score and damage that surface. Second, all the pressure of the clamp is on the threads of the pull member and the wing nut, and therefore, the threads tend to become stripped, especially when a wrench is used to tighten the wing nut. This damages both the wing nut and the pull member, and these parts must then be replaced. Third, the wing nut does not permit a quick release of the clamp from its closed to its fully open position. Fourth, it is difficult to judge, when tightening the wing nut, whether the proper degree of tightness of the clamp has been obtained. Fifth, the wing nut is awkward to handle and difficult to tighten sufficiently to fully close the clamp without using a wrench.
British patent Underwood Nos. 6,829/1911 and Taylor No. 923,974, published Apr. 18, 1963, and the following U.S. patents each disclose a clamping device that includes a cam member with a peripheral surface eccentrically disposed about an axis:
U.S. Pat. No. 694,389, granted Mar. 4, 1902, to A. Klitsche;
U.S. Pat. No. 1,049,642, granted Jan. 7, 1913, to W. C. Baesel;
U.S. Pat. No. 1,397,930, granted Nov. 22, 1921, to J. L. Jefferies;
U.S. Pat. No. 2,398,962, granted Apr. 23, 1946, to B. F. Randrup;
U.S. Pat. No. 2,422,865, granted June 24, 1947, to J. I. Tucker;
U.S. Pat. No. 2,650,809, granted Sept. 1, 1953, to L. P. Wansink et al;
U.S. Pat. No. 3,136,020, granted June 9, 1964, to C. B. Baker;
U.S. Pat. No. 3,159,393, granted Dec. 1, 1964, to J. Villano; and
U.S. Pat. No. 3,896,526, granted July 29, 1975, to T. R. Joiner.
Taylor, British Pat. No. 923,974, discloses a clamp with a cam lever for pulling a pull member to in turn pull one arm of a U-shaped clamp body toward the second arm of such body. The cam lever includes a cam member with a peripheral surface disposed about an axis, said peripheral surface having a plurality of edge portions each of which is a different set perpendicular distance from the axis.
Randrup, U.S. Pat. No. 2,398,962, discloses a clamp in which a cam lever is threadedly connected to the threaded shaft of a T-shaped member. This shaft extends through the members to be clamped together. The cam surface of the lever apparently has a constant radius. The clamp is tightened by rotating the lever about the longitudinal axis of the pull member.
Joiner, U.S. Pat. No. 3,896,526, discloses a friction binder for vertical filling of sheet material the includes a cam lever that is pivotally connected to a pull member.
The above patents and the prior art that is discussed and/or cited therein should be studied for the purpose of putting the present invention into proper perspective relative to the piror art.